1. Field of the Invention
The present invention relates to an iron-type golf club head, particularly to a golf club head of which at least a face is made of an iron material, and at least a face surface is carburized.
2. Description of the Related Art
As a material for an iron-type golf club head, a soft iron, stainless steel, a beryllium alloy, a copper alloy, and the like, has been used. In addition, an iron golf club head of a composite type whose peripheral edge section is made of stainless steel, and to which a face plate made of a titanium alloy is attached has come into widespread use in recent years. Hereinbelow, an iron-type golf club head is often referred to as an “iron head.”
An iron head made of pure iron whose purity falls within a range of 99.93 to 99.97% is disclosed in JP-A-63-229078. In lines 1 to 8, upper left column, page 3 of the specification, it is disclosed that pure iron has great elongation and drawing ratio, and is superior in malleability, accordingly, a contact area between a golf ball and a face of the iron head made of pure iron is expanded, and a contact time is elongated, thereby enhancing directional stability of a hit ball.
Forming a surface-hardening layer on an iron head made of a soft iron material by means of carburizing or nitriding is disclosed in JP-A-8-206260.
Application of plasma carburizing or gas carburizing to an iron head made of a structural alloy steel, stainless steel, titanium, or a titanium alloy steel so as to increase surface hardness, thereby enhancing a carry distance of a hit ball is disclosed in JP-A-10-5376 (paragraph Nos. [0008] through [0017]).
A golf club head which is made of titanium or a titanium alloy and whose surface is hardened by means of carburizing or nitriding so as to have a surface hardness of HV (hardness value of Vickers) 450 to 1,000 is disclosed in JP-A-10-216275.
A material generally employed for a golf club head, such as a structural alloy steel, stainless steel, or a titanium alloy steel, has a high hardness of about HV 300 to 400. Meanwhile, pure titanium is of a hardness similar to that of soft iron, about HV 110 to 150.
As compared with an iron head made of stainless steel, an iron head made of pure iron is lower in material hardness and produces a softer ball-hit feeling. However, because of low abrasive resistance, the iron head made of pure iron is easily damaged on its surface, and angular edges of score lines (lateral grooves on a face surface) are rounded at an early stage, thereby making it difficult to impart spin to a hit ball. In addition, when the iron head is used in such a rounded condition, micro deformations caused by impacts applied at the time of hitting a ball are accumulated, thereby changing a loft angle and the like.
Increasing surface hardness of an iron head made of a soft iron material or an alloy steel by means of carburizing is disclosed in the above-mentioned JP-A-8-206260 and JP-A-10-5376, however, application of carburizing to an iron head made of a pure iron material is not described therein.
The golf club head disclosed in the above-mentioned JP-A-10-216275 is for a driver-type golf club. Accordingly, when an iron head is imparted with a surface hardness of HV 450 to 1,000 as disclosed in the specification, surface hardness of a face surface thereof becomes too high, resulting in an inferior ball-hit feeling.